1. Field of the Invention
The present invention relates to a clock spring interconnector for electrically connecting a fixed member and a movable member by use of flexible cable such as a flat cable, and more particularly to a clock spring interconnector suitable for use with a steering system for a vehicle.
2. Description of the Prior Art
In a clock spring one end of a flexible cable such as a flat cable is secured to a fixed member whereas the other end thereof is secured to a movable member so that when the movable member is rotated, the flexible cable is wound on or unwound from the movable member to thereby rotate the movable member through a predetermined amount. The clock spring interconnector is used for a steering system for a vehicle or the like.
FIGS. 4 to 6 show a conventional clock spring interconnector for an automobile of this kind. FIG. 4 is an exploded perspective view, FIG.5 is a longitudinal sectional view and FIG. 6 is a plan view with a part of the movable member omitted. In these figures, reference numeral 1 designates a movable member. The movable member 1 has in its central portion a rotational tube 3 suspended having an axial inserting hole 2, and a cylindrical holder 4 is arranged externally of the rotational tube 3. The holder 4 has a vertically extending slit 4a and a recess 4b in an inner surface thereof, the holder 4 being fixedly mounted on a top place of the movable member 1 in a relation spaced apart from the outer peripheral surface of the rotational tube 3.
Reference numeral 5 designates a flat cable in which a plurality of conductors formed of copper foil or the like are laminated by two base films having a flexibility such as polyethylene terephthalate (PET). One end of the flat cable 5 reaches the recess 4b passing through the slit 4b of the holder 4 and thereafter is turned back at right angles through a folding line approximately at 45 degrees within the recess 4b and finally extended outside the movable member 1. At the aforesaid turned-back portion, the flat cable 5 is divided into two extended-out portions 5a and 5b along the lengthwise, the extended-out portions 5a and 5b each being folded back at positions superposed with each other. These portions 5a and 5b are snap-coupled to each other and held and fixed between first and second stoppers 6 and 7 secured to the top plate of the movable member 1. In this state, a taper portion 6a formed in the first stopper 6 is inserted into the turned-back portion of both the extended-out portions 5a and 5a.
Reference numeral 8 designates a fixed member. The fixed member 8 is formed in the central portion thereof with a center hole 9 in which a rotary tube 3 of the movable member 1 is rotatably snapped in, and the fixed member 8 is further formed in the outer peripheral portion thereof with an outer ring wall 10 for receiving therein the flat cable 5. The outer ring wall 10 is formed with a projecting guide portion 11 directed obliquely and downwardly. The other end of the flat cable 5 is turned back at right angles internally of the outer ring wall 10 and thereafter extended externally of the fixed member 8 along the guide portion 11. A positioning mechanism 13 provided with a gear 12 is provided on the outer ring wall 10, the gear 12 being engaged with an engaging projection 14 provided on the outer periphery of the movable 1 so that the gear 12 is rotated through a predetermined angle.
The clock spring interconnector is roughly formed as described above and used, in various equipment, for example, with the movable member 1 mounted on the side of the steering wheel of the steering system and with the fixed member 8 mounted on the side of the bearing of the steering shaft. In this case, when the steering wheel (movable member 1) is rotated toward one side, the flat cable 5 is wound toward the holder (inner ring wall) whereas when the steering wheel is rotated toward the other side, the flat cable 5 is wound toward the outer ring wall 10. In either state, the electric connection between the movable member 1 and the fixed member 8 is maintained through the flat cable 5. Since the gear 12 comes into contact with the engaging projection 14 and is rotated through a predetermined angle as the movable member 1 rotates for once, marks can be marked on a specific tooth of the gear 12 and a case side of a positioning mechanism, for example, to prevent an occurrence of a difference in rotational amount between the normal and reverse directions of the flat cable 5 to prevent a breakage or buckling of the flat cable 5.
However, even if the positioning mechanism 13 is provided between the movable member 1 and the fixed member 8, as mentioned above, it is difficult to completely eliminate an erroneous mounting. For example, the movable member 1 is sometimes mounted in a state where the movable member 1 is rotated in either one direction from a neutral position. In the case where erroneous mounting is made so that the rotational amount of the movable member in the unwinding direction of the flat cable 5 is lessened, when the movable member 1 is rotated in that direction in an amount in excess of a predetermined amount, a portion in the vicinity of the inner peripheral end of the flat cable 5 is inverted and bended, as shown in FIGS. 7(a), 7(b) and 7(c), resulting causes of lowering a reliability of connection such as a breakage of conductor, peeling of film, etc.
A clock spring interconnector has been proposed as disclosed in Japanese Utility Model Application Laid-Open Publication No. 168581/1987, in which an elastic tongue formed from a resin sheet or the like is provided along the flat cable to prevent the flat cable from being inverted. This proposal, however, poses a problem in that since the winding diameter of the flat cable to the inner ring wall substantially increases due to the thickness of the elastic tongue, the limited rotational frequency of the movable member is smaller than the case of using no elastic tongue.